Existing laparotomy surgery, endoscopic surgery, and robot-assisted surgery are all categorized as surgical techniques performed in a condition where an internal organ is exposed to gas and gravity. In such a conventional surgical technique, the internal organ should be treated against gravity, which in turn requires that instruments, such as a forceps, for treating the organ have a certain degree of strength. As a result of this, the extent to which the diameter of the forceps may be minimized is limited. Further, when an ultrasonic diagnosis is conducted during a surgical operation, position of an ultrasound probe is restricted to specific locations.
Under the circumstances, it has been suggested that surgical operations be performed while a body cavity is perfused with a fluid such as an isotonic solution. For example, Patent Literature 1 discloses an apparatus for performing continuous perfusion and discharge of a physiological fluid for perfusion into and out of a body tissue or cavity of a human or an animal. On the other hand, Patent Literature 2 discloses a trocar suitable for perfusing a body cavity with a fluid. The trocar has an inner tube that constitutes a path for an endoscope and an outer tube that is concentrically arranged so as to cover an outer periphery of the inner tube. An end surface of the outer tube is provided with a fluid outlet for discharging the fluid and a fluid inlet for drawing the fluid.